The invention relates generally to converter circuits, and particularly to a converter circuit with adjustable DC bus voltage.
Wide ranges of equipment utilizing various converter circuits are known, such as electric motor drive systems used in factory automation systems, power generation systems and so forth. Typically an electric motor drive is connected to a power source, most often the power grid, and operates to provide electrical power to a load in a controlled manner.
In alternating current (AC) motor drive systems, electrical power is converted from an AC power source into direct current (DC) power via a rectifier. The DC power is then converted via a power converter coupled to the converter through a DC bus into AC power with controlled frequency, phase and amplitude, which may be applied to drive the electric motor.
Typically, the electric motor drive systems have a fixed upper DC bus voltage limit. When driving certain types of loads, such as inertial loads, power may be regenerated by motion of the load that flows into the DC bus, potentially raising the DC bus voltage to within a range near or just below this limit. In systems that cannot channel this regenerated power to the power grid, this excess power regenerated by the electric motor may be absorbed and subsequently dissipated through shunt resistors that can be electrically coupled across the DC bus. Because these resistors simply convert the power to heat, their use may substantially reduce the efficiency of such systems. Furthermore, components of such systems may be subjected to substantially high temperatures and may require additional cabinet cooling.
Accordingly, it would be desirable to develop a motor drive system having some mechanism for reducing the amount of power dissipated by shunt resistors in this manner to enhance efficiency and reliability of such systems.